I've beaten all the standard maps on "very clever" but I can't beat this one.

You start with a struggling colony in the centre and that's about it. The browns have a massive advantage starting in a relatively chaotic peninsula on the left hand side lower. Even if you do manage to get something going in the centre you're constantly fighting on all sides until the browns sweep in and win.

I got as far as the late 20's, and ended up having to keep switching focus from a yellow(4) empire in the east, a brown(6) one to the southwest, and light green(5) to the north. It could have easily been dark green(3) in the north, depending on my decisions, and whether brown is aggressive against them or me.

Surrender offer at turn 30, turned it down, but still have a strong-ish yellow to stomp out, and the very southern tip of brown to clear out. The key is sort of drawing brown to overextend north of your central empire, cut that push, let them do it again while you establish and fortify a good border to your eastern edge, re-cutting brown, then driving into their peninsula, taking land faster than the other players nibble at you. Before another empire becomes a true threat, fortify your holdings in brown, and turn to face the largest threat.

I don't know that I had any castles until I was holding off yellow to the east... the key is to actually not dive straight into the merger in the center. You win or lose this map in the first five turns or so, and the first three or four determine how long it takes you to win or lose. And always wait as long as possible to build knights, as they are a huge drain on resources. Think of it this way: A peasant costs two points to maintain for a turn, so in two turns it can capture enough land to pay its upkeep, after that it is profit. A knight has to capture a hex every turn for 18 turns to start paying its keep, so by the time you get one, it may never pay for itself. That's a simplified way of looking at it, as it doesn't account for losing territory on a given turn, but it makes a nice baseline. The initial cost of units is relatively insignificant, especially for the higher ups. Barons, for instance, cost more in upkeep per turn than they cost to build.

I'm not sure I get you Legacy. Knights cost 6 per go and as you will almost certainly convert 2 peasants to a knight, the net extra drain on your resources is only 2. So I can't see how it takes 18 turns to repay its cost. In any case, if you wait too long, your neighbour will undoubtedly have one and disect your holdings. Your advice would lead to an early bath I fear.

The point at which you convert 2 peons to a knight is a personal one and depends on your ability to expand using peasants and your fear of the folks next door. There comes a point when you can't expand as there are peasants and huts everywhere: to continue you need a knight.

In my case, a castle was essential to guard the hut from an early green knight while I expanded Northward.